Leetcode Problem difficulty level and frequency table

http://yumei165.blogspot.com/2013/04/leetcode-problem-difficulty-level-and.html

Source: http://leetcode.cloudfoundry.com/
Author: peking2 

Leetcode Questions

Id	Question	Difficulty	Freqency	Data Structures	Algorithms
1	Two Sum	2	5	array set	sort two pointers
2	Add Two Numbers	3	4	linked list	two pointers math
3	Longest Substring Without Repeating Characters	3	2	string hashtable	two pointers
4	Median of Two Sorted Arrays	5	3	array	binary search
5	Longest Palindromic Substring	4	2	string
6	ZigZag Conversion	3	1	string
7	Reverse Integer	2	3		math
8	String to Integer (atoi)	2	5	string	math
9	Palindrome Number	2	2		math
10	Regular Expression Matching	5	3	string	recursion dp
11	Container With Most Water	3	2	array	two pointers
12	Integer to Roman	3	4		math
13	Roman to Integer	2	4		math
14	Longest Common Prefix	2	1	string
15	3Sum	3	5	array	two pointers
16	3Sum Closest	3	1	array	two pointers
17	Letter Combinations of a Phone Number	3	3	string	dfs
18	4Sum	3	2	array
19	Remove Nth Node From End of List	2	3	linked list	two pointers
20	Valid Parentheses	2	5	string	stack
21	Merge Two Sorted Lists	2	5	linked list	sort two pointers merge
22	Generate Parentheses	3	4	string	dfs
23	Merge k Sorted Lists	3	4	linked list heap	sort two pointers merge
24	Swap Nodes in Pairs	2	4	linked list
25	Reverse Nodes in k-Group	4	2	linked list	recursion two pointers
26	Remove Duplicates from Sorted Array	1	3	array	two pointers
27	Remove Element	1	4	array	two pointers
28	Implement strStr()	4	5	string	two pointers KMP rolling hash
29	Divide Two Integers	4	3		binary search math
30	Substring with Concatenation of All Words	3	1	string	two pointers
31	Next Permutation	5	2	array	permutation
32	Longest Valid Parentheses	4	1	string	dp
33	Search in Rotated Sorted Array	4	3	array	binary search
34	Search for a Range	4	3	array	binary search
35	Search Insert Position	2	2	array
36	Valid Sudoku	2	2	array
37	Sudoku Solver	4	2	array	dfs
38	Count and Say	2	2	string	two pointers
39	Combination Sum	3	3	array	combination
40	Combination Sum II	4	2	array	combination
41	First Missing Positive	5	2	array	sort
42	Trapping Rain Water	4	2	array	two pointers stack
43	Multiply Strings	4	3	string	two pointers math
44	Wildcard Matching	5	3	string	recursion dp greedy
45	Jump Game II	4	2	array
46	Permutations	3	4	array	permutation
47	Permutations II	4	2	array	permutation
48	Rotate Image	4	2	array
49	Anagrams	3	4	string hashtable
50	Pow(x, n)	3	5		binary search math
51	N-Queens	4	3	array	dfs
52	N-Queens II	4	3	array	dfs
53	Maximum Subarray	3	3	array	dp
54	Spiral Matrix	4	2	array
55	Jump Game	3	2	array
56	Merge Intervals	4	5	array linked list red-black tree	sort merge
57	Insert Interval	4	5	array linked list red-black tree	sort merge
58	Length of Last Word	1	1	string
59	Spiral Matrix II	3	2	array
60	Permutation Sequence	5	1		permutation math
61	Rotate List	3	2	linked list	two pointers
62	Unique Paths	2	3	array	dp
63	Unique Paths II	3	3	array	dp
64	Minimum Path Sum	3	3	array	dp
65	Valid Number	2	5	string	math
66	Plus One	1	2	array	math
67	Add Binary	2	4	string	two pointers math
68	Text Justification	4	2	string
69	Sqrt(x)	4	4		binary search
70	Climbing Stairs	2	5		dp
71	Simplify Path	3	1	string	stack
72	Edit Distance	4	3	string	dp
73	Set Matrix Zeroes	3	5	array
74	Search a 2D Matrix	3	3	array	binary search
75	Sort Colors	4	2	array	sort two pointers
76	Minimum Window Substring	4	2	string	two pointers
77	Combinations	3	4		combination
78	Subsets	3	4	array	recursion combination
79	Word Search	3	4	array	dfs
80	Remove Duplicates from Sorted Array II	2	2	array	two pointers
81	Search in Rotated Sorted Array II	5	3	array	binary search
82	Remove Duplicates from Sorted List II	3	3	linked list	recursion two pointers
83	Remove Duplicates from Sorted List	1	3	linked list
84	Largest Rectangle in Histogram	5	2	array	stack
85	Maximal Rectangle	5	1	array	dp stack
86	Partition List	3	3	linked list	two pointers
87	Scramble String	5	2	string	recursion dp
88	Merge Sorted Array	2	5	array	two pointers merge
89	Gray Code	4	2		combination
90	Subsets II	4	2	array	recursion combination
91	Decode Ways	3	4	string	recursion dp
92	Reverse Linked List II	3	2	linked list	two pointers
93	Restore IP Addresses	3	3	string	dfs
94	Binary Tree Inorder Traversal	4	3	tree hashtable	recursion morris stack
95	Unique Binary Search Trees II	4	1	tree	dp dfs
96	Unique Binary Search Trees	3	1	tree	dp
97	Interleaving String	5	2	string	recursion dp
98	Validate Binary Search Tree	3	5	tree	dfs
99	Recover Binary Search Tree	4	2	tree	dfs
100	Same Tree	1	1	tree	dfs
101	Symmetric Tree	1	2	tree	dfs
102	Binary Tree Level Order Traversal	3	4	tree	bfs
103	Binary Tree Zigzag Level Order Traversal	4	3	queue tree	bfs stack
104	Maximum Depth of Binary Tree	1	1	tree	dfs
105	Construct Binary Tree from Preorder and Inorder Tr	3	3	array tree	dfs
106	Construct Binary Tree from Inorder and Postorder T	3	3	array tree	dfs
107	Binary Tree Level Order Traversal II	3	1	tree	bfs
108	Convert Sorted Array to Binary Search Tree	2	3	tree	dfs
109	Convert Sorted List to Binary Search Tree	4	3	linked list	recursion two pointers
110	Balanced Binary Tree	1	2	tree	dfs
111	Minimum Depth of Binary Tree	1	1	tree	dfs
112	Path Sum	1	3	tree	dfs
113	Path Sum II	2	2	tree	dfs
114	Flatten Binary Tree to Linked List	3	3	tree	recursion stack
115	Distinct Subsequences	4	2	string	dp
116	Populating Next Right Pointers in Each Node	3	3	tree	dfs
117	Populating Next Right Pointers in Each Node II	4	2	tree	dfs
118	Pascal's Triangle	2	1	array
119	Pascal's Triangle II	2	1	array
120	Triangle	3	1	array	dp
121	Best Time to Buy and Sell Stock	2	1	array	dp
122	Best Time to Buy and Sell Stock II	3	1	array	greedy
123	Best Time to Buy and Sell Stock III	4	1	array	dp
124	Binary Tree Maximum Path Sum	4	2	tree	dfs
125	Valid Palindrome	2	5	string	two pointers
126	Word Ladder II	1	1
127	Word Ladder	3	5	graph	bfs shortest path
128	Longest Consecutive Sequence	4	3	array
129	Sum Root to Leaf Numbers	2	4	tree	dfs
130	Surrounded Regions	4	3	array	bfs dfs
131	Palindrome Partitioning	3	4	string	dfs
132	Palindrome Partitioning II	4	3	string	dp

Emacs basis

2. C-x C-c: exit

3. C-v: next screen M-v: previous screen

C-l: moving the text around the cursor to the center of this screen

4. C-p: previous line C-n: next line

C-f: forward a character C-b: backward a character

M-f: forward a word M-b: backward a word

C-a: moving to the beginning of a line C-e: moving to the end of a line

M-a: moving to the beginning of a sentence M-e: moving to the end of a sentence

Note: Meta characters are used for operations related to the units defined by language (words, sentences, paragraphs), while Control characters operate on basic units that are independent of what you are editing (characters, lines, etc.)

5. M-<: home="" m-="" moving="" of="" text="" the="" to="" whole="">: moving to end of the whole text

6. numeric argument: C-u and then the digits before typing the command. it means repeatedly executing the command.

Excetion: e.g. C-u 8 C-v scrolls screen by 8 lines instead of 8 screens.

7. C-g: discard a command

8. C-x 1: remove other windows

9 delete or kill operations

C-d: delete next character M-d: kill next word

C-k: kill from current position to end of line M-k: kill from current position to end of sentence

: delete char just before cursor M-: kill word just before cursor

general killing method: moving to one end of the text to be killed, typing C-, moving to the other end, typing C-w.

killed text can be brought back, which is called "yanking".

10. yanking---reinsert the last killed text.

C-y

finding most recent killing: C-y

finding some killing: C-y and then M-y untill you find what you want

11 undo

C-x u

12 file operations

C-x C-f : find file C-x C-s: save file

13 buffers

C-x C-b : list buffers

C-x b: switch buffer

C-x s: save some buffer

14 minimize windows C-z

15 replace strings

M-x repl sstring1string2: string1 is replaced by string2

16 major modes: fundamental, lisp, text

17 turn on "auto fill mode"

M-x auto fill mode